1. Field of the Invention
The present invention relates generally to techniques for setting operating characteristics of switch-mode power supplies (SMPSs), and more specifically, to an SMPS controller integrated circuit that internally adjusts operating characteristics parameters from specified filter component information.
2. Background of the Invention
Switching power converters, referred to as switch-mode power supplies (SMPSs) are currently in widespread use for applications such as systems power supplies, AC power inverters, as well as localized power supplies, also known as point-of-load (PoL) supplies, such as voltage regulator modules (VRMs) for microprocessors. In an SMPS, one or more magnetic storage elements such as inductors or transformers are energized and interrupted by a switching circuit and the stored energy is typically periodically transferred to one or more capacitive storage elements. The output voltage or output current (or an analog of the output voltage/current) of the SMPS is sensed by a sensing circuit and used to control the switching circuit so that voltage or current regulation is provided over a variety of input voltage, output load and temperature variation ranges.
A compensation circuit or “compensator” is provided in the feedback and/or feed-forward paths of the converter between the sensing circuit and the switching circuit and sets the control response of SMPS to the sensed output voltage and/or current. The compensator modifies the closed-loop response of the converter to ensure that the converter is stable, i.e., the output is well-behaved, and to ensure desired operating conditions. The compensator is typically provided by a controller integrated circuit (IC) that typically receives output current and/or voltage information as well as input voltage information, and generates one or more output control signals to control the SMPS switching circuits. In analog compensation schemes, external components are used in conjunction with internal amplifiers of the controller IC to provide the compensator filter.
An integrated circuit controller designed for general purpose use in a variety of applications generally includes a compensator that can be adjusted over a wide range of frequency and phase response characteristics. In traditional analog compensator implementations, external terminals of the controller IC expose circuit nodes of a feedback signal chain that implements the compensator. Passive components, typically resistors and capacitors connected to one or more terminals of the integrated circuit provide a network that directly determines the compensator frequency response according to the interaction of the components in the network with the internal elements of the compensator. For example, poles and zeros of an amplifier stage internal to the IC can be set by RC feedback and input networks connected to an output and input of the amplifier that are connected to terminals of the IC. The values of the resistors and capacitors are determined from the desired locations of the poles and zeros of the compensator response, which are first determined from the external components and line/load conditions of the actual SMPS implementation.
In digital power control applications, the compensator is generally a digital compensator provided by a digital signal processing block or dedicated filter logic units. Coefficients, which are floating-point or fixed-point numbers that dictate the discrete-time computations needed to provide the response, are provided to the controller IC by techniques such as auto-compensation start-up calibration, by programming non-volatile (NV) storage within the controller IC with the coefficients, which are read at start-up, or by reading the coefficients from an external storage device. The coefficient values are typically determined by a computer program that is used by a power supply designer to specify the component values of the SMPS external to the controller, such as the inductances, capacitances and resistances of the filter components external to the controller IC, which are then used by the program to compute the coefficients required to obtain a particular response selected by the designer.
In practice, it is desirable to be able to integrate and initially test an SMPS design without having to use a design program to determine the initial compensation values and program those values into a prototype unit. In many instances, an SMPS controller IC is being evaluated in a particular application without the luxury of extended engineering design time or without the availability of all of the requisite tools. However, due to the wide ranges of external component values for a typical controller IC, stable operation, and thus useful evaluation cannot be guaranteed without some compensation based upon the actual external component values selected for an SMPS design. Further, every time a component value, type or operating parameter (e.g., input voltage) is changed in an SMPS design, the computer program and any necessary NV storage programming tools must then be used to update the compensation coefficients.
Finally, other operating parameters of the SMPS are dependent on the filter component values, such as output ripple, transient response, etc., and therefore operational characteristics other than compensation of the SMPS are affected when filter component values change.
Therefore, it would be desirable to provide a digitally-compensated SMPS controller IC that can be compensated without resort to design programs that determine the compensator coefficients. It would further be desirable to provide such an SMPS controller IC that does not require a NV storage programmer or external storage device for initialization. It would further be desirable to provide an SMPS controller IC in which other operating characteristics dependent on filter component values or types can be controlled to provide and maintain desired operation of an SMPS.